[AArch64][CodeGen] Fix illegal register aliasing bug for mops instrs (#88869)

A bug was found where mops instructions were being generated that
aliased the source and size registers. This is unpredictable behaviour.
This patch uses the earlyclobber constraint on the input source
register so that it doesn't alias with the size register. Also a test is
introduced which checks affected instructions can't violate this
constraint.

Author: nasherm

llvm/lib/Target/AArch64/AArch64InstrInfo.td

@@ -9486,7 +9486,7 @@ let Predicates = [HasMOPS], Defs = [NZCV], Size = 12, mayStore = 1 in {
   let mayLoad = 0 in {
     def MOPSMemorySetPseudo  : Pseudo<(outs GPR64common:$Rd_wb, GPR64:$Rn_wb),
                                       (ins GPR64common:$Rd, GPR64:$Rn, GPR64:$Rm),
-                                      [], "$Rd = $Rd_wb,$Rn = $Rn_wb">, Sched<[]>;
+                                      [], "$Rd = $Rd_wb,$Rn = $Rn_wb,@earlyclobber $Rn_wb">, Sched<[]>;
   }
 }
 let Predicates = [HasMOPS, HasMTE], Defs = [NZCV], Size = 12, mayLoad = 0, mayStore = 1 in {

llvm/test/CodeGen/AArch64/mops-register-alias.ll

@@ -0,0 +1,21 @@
+; RUN: llc -O1 -mtriple=aarch64-none-linux-gnu -mattr=+mops -o - %s  | FileCheck %s
+
+define void @call_memset_intrinsic() #0 {
+; CHECK-LABEL: call_memset_intrinsic:
+; CHECK:       // %bb.0: // %entry
+; CHECK:         setp [x{{[0-9]+}}]!, x{{[0-9]+}}!, x{{[0-9]+}}
+; CHECK-NOT:     setp [x{{[0-9]+}}]!, x[[REG:[0-9]+]]!, x[[REG]]
+; CHECK-NEXT:    setm [x{{[0-9]+}}]!, x{{[0-9]+}}!, x{{[0-9]+}}
+; CHECK-NOT:     setm [x{{[0-9]+}}]!, x[[REG:[0-9]+]]!, x[[REG]]
+; CHECK-NEXT:    sete [x{{[0-9]+}}]!, x{{[0-9]+}}!, x{{[0-9]+}}
+; CHECK-NOT:     sete [x{{[0-9]+}}]!, x[[REG:[0-9]+]]!, x[[REG]]
+entry:
+
+    %V0 = alloca [65 x i8], align 1
+    call void @llvm.memset.p0.i64(ptr noundef nonnull align 1 dereferenceable(64) %V0, i8 64, i64 64, i1 false)
+    %add.ptr = getelementptr inbounds i8, ptr %V0, i64 64
+     call void @llvm.memset.p0.i64(ptr noundef nonnull align 1 dereferenceable(64) %add.ptr, i8 64, i64 64, i1 false)
+    ret void
+}
+
+attributes #0 = { "target-cpu"="generic" "target-features"="+mops,+strict-align,+v9.3a" }

llvm/test/MC/AArch64/armv9.3a-mops-register-aliasing.s

@@ -0,0 +1,15 @@
+// RUN: not llvm-mc -triple aarch64 -mattr=+mops < %s 2>&1 | FileCheck %s
+
+  setp  [x0]!, x1!, x1
+  setm  [x0]!, x1!, x1
+  sete  [x0]!, x1!, x1
+
+// CHECK:      error: invalid SET instruction, source and size registers are the same
+// CHECK-NEXT:   setp  [x0]!, x1!, x1
+// CHECK-NEXT:         ^
+// CHECK-NEXT: error: invalid SET instruction, source and size registers are the same
+// CHECK-NEXT:   setm  [x0]!, x1!, x1
+// CHECK-NEXT:         ^
+// CHECK-NEXT: error: invalid SET instruction, source and size registers are the same
+// CHECK-NEXT:   sete  [x0]!, x1!, x1
+// CHECK-NEXT:         ^